A hybrid vehicle such as a plug-in hybrid vehicle is equipped with a battery as well as an internal combustion engine and an electric motor as power sources for traveling. The battery supplies electric power to the electric motor and is electrically charged with electric power from an external power source.
In this type of hybrid vehicles, it is desired that the electric power remaining in the battery is consumed to its lower-limit value at the time when the battery is to be charged next time from an external power source so as to lower the pollution and to save energy. On the other hand, if the amount of electric power remaining in the battery reaches the lower-limit value on the way to a battery charging point, the vehicle must travel thereafter with only the internal combustion engine. This makes it difficult to lower the pollution or to save energy. Besides, this decreases the traveling performance of the vehicle.
To counter this drawback, U.S. Pat. No. 5,892,346 (JP 2004-7969A) proposes that, based on a distance from a start point which is a charge-possible point where the battery is charged on an optimum route up to a destination, target amounts of electric power to remain in the battery are set at various points in-travel. Thus, no electric power remains in the battery at the destination point, and the electric power of the battery is supplied to the electric motor based on the target amounts of electric power remaining in the battery.
However, it is difficult to realize the target amounts of electric power remaining in the battery by the above technology. This is because the traveling mode up to the designation point varies every time of traveling. Control processing becomes very complicated for determining the time points for executing the drive of the vehicle by the internal combustion engine, for executing the drive of the vehicle by the electric motor and for executing the charging of the battery by the internal combustion engine to meet the setting.